The present invention relates to reciprocating piston fluid compression devices such as hermetic refrigerant compressors, particularly with regard to quieting same.
Fluid compression devices such as, for example, refrigerant compressors, receive a gas at a suction pressure and compress it to a relatively higher, discharge pressure. Depending on the type of compression device, the work exerted on the gas in compressing it is characterized by a series of intermittently exerted forces on the gas, the magnitude of these forces normally varying from zero to some maximum value. For example, in a cylinder of a reciprocating piston type compressor, this force ranges from zero at the piston""s bottom dead center (BDC) position, to a maximum at or near the piston""s top dead center (TDC) position, at which the pressure of the compressed gas is respectively at a minimum pressure (i.e., substantially suction pressure) and a maximum pressure (i.e., substantially discharge pressure). Some quantity of the gas is discharged from the cylinder as the piston assumes new positions as it advances from BDC to TDC, and thus the compressed gas flowing from the cylinder is not at a uniform pressure. Rather, the gas which flows from the cylinder, which is generally referred to as being at discharge pressure, actually has many different pressures.
Pulses of higher discharge pressure result in the compressed gas flowing from the cylinder, these pulses being in the portion of the flowing gas which leaves the cylinder as the piston approaches or reaches TDC. As the piston cycles in its cylinder, regular, equally distributed patterns of these pulses are created in the compressed gas which flows through a conduit, tube or line leading from the compression mechanism. The pulsating flow of compressed gas through this discharge line may be represented by sine waves of various frequencies and having amplitudes which may vary with changes in the quality of the refrigerant; these changes are effected by changes in refrigerant type, temperature or pressure. Pulsations at certain frequencies may be more noticeable, and thus more objectionable, than others.
Further, the nominal discharge pressure, i.e., the pressure at which the compressed gas is generally considered to be, will also vary with refrigerant quality. The frequency of these high pressure pulses in the compressed gas flowing through the discharge line, however, has a substantially constant frequency which directly correlates to the speed at which the gas is compressed in the cylinder, and the number of cylinders in operation. This frequency is referred to as the primary pumping frequency, and is generally the lowest frequency exhibited by the pressure pulsations in the compressed gas.
The amplitude of the pressure pulses at the primary pumping frequency tend to be the largest in the compressed gas flow. Because the primary pumping pulses are at low frequencies and large amplitudes, they are often the primary cause of objectionable noise or vibration characteristics in compressors or the refrigeration systems into which these compressors are incorporated. These systems normally also include at least two heat exchangers, a refrigerant expansion device, and associated refrigerant lines which link these components into a closed loop relationship. Pressure pulsations at other, higher frequencies have amplitudes which are relatively smaller, but certain of these pressure pulsations may also be objectionable. Further, some objectionable pressure pulsations may establish themselves in the conduits or lines which convey refrigerant substantially at suction pressure to the compression mechanism.
Substantial effort has been expended in attempting to quiet these pressure pulses in addressing noise or vibration concerns, and it is known to provide mufflers in the discharge or suction lines to help resolve these issues. These mufflers may be of the expansion chamber type, in which a first refrigerant line portion opens directly into a chamber, wherein the amplitude and/or frequency of at least one of the pulses may be altered, and from which the refrigerant exits through a second line portion. Further, it is known that the discharge chamber in the head of a reciprocating piston compressor can also serve as a type of expansion chamber muffler. An expansion chamber type muffler of any type is not entirely satisfactory, however, for it may cause a substantial pressure drop in the gas as it flows therethrough, resulting in compressor inefficiency. Further, such mufflers may not provide sufficient attenuation required by the application.
An alternative to an expansion chamber type of muffler is what is well known in the art as a Helmholtz resonator type of muffler wherein the wall of a portion of the discharge pressure line may be provided with a plurality of holes, that portion of the discharge line is sealably connected to a shell which defines a resonance chamber, the holes in the discharge line providing fluid communication between the interior of the discharge line and the resonance chamber. The size and/or quantity and/or axial spacing of these holes, and the volume of the resonance chamber, are variably sized to tune a Helmholtz resonator to a particular frequency, and the amplitude of pulses at that frequency are thereby attenuated. Compared to an expansion chamber type of muffler, a Helmholtz muffler provides the advantage of not causing so significant a pressure drop in the fluid flowing therethrough; thus compressor efficiency is not compromised to the same degree.
Although a Helmholtz resonator may be effective for attenuating the amplitude of fluid pulses having shorter wavelengths, in which case the resonator extends axially over at least a substantial portion of the pulse wavelength, prior Helmholtz resonator arrangements may not be effective for attenuating the amplitude of fluid pulses having longer wave lengths. As mentioned above, the primary pumping frequency tends to be rather low, the primary pumping pulses cyclically distributed over a rather long wavelength. By way of the example of a single-speed hermetic reciprocating piston type compressor, the motor thereof rotates at a speed which is directly correlated to the frequency of the alternating current (AC) electrical power which drives it. In the United States, AC power is provided at 60 cycles/second. The electrical current is directed through the windings of the motor stator, and electromagnetically imparts rotation to the rotor disposed inside the stator. The crankshaft of the compressor is rotatably fixed to the rotor and drives the reciprocating piston, which compresses the refrigerant. Thus the primary pumping frequency is at or near 60 cycles per second. The speed of sound in refrigerant gas at the discharge temperature and pressure of this example is 7200 inches per second. Thus, in accordance with the equation:
c/f=xcexxe2x80x83xe2x80x83(1)
where speed xe2x80x9ccxe2x80x9d is 7200 inches per second and frequency xe2x80x9cfxe2x80x9d is 60 cycles per second, for the above example wavelength xe2x80x9cxcexxe2x80x9d of the primary pumping pulse is 120 inches. Notably, should the compressor be of the two cylinder variety, twice as many primary pumping pulses will be issued per revolution of the crankshaft; thus xcex will then be 60 inches. It can be readily understood by those of ordinary skill in the art that simply providing a single Helmholtz resonator in the discharge line may be largely ineffective for attenuating the amplitude of a pulse which has such a long wavelength, for the point(s) of maximum pulse amplitude, which ought to be coincident with the resonator, may be too far separated. In order for a single Helmholtz resonator to quiet a pulse having such a long wavelength, the resonator would be far too long to facilitate easy packaging within the refrigerant system, let alone within the hermetic compressor housing.
What is needed is a noise attenuation system for a compression device which effectively addresses the noise and vibration issues associated with pressure pulses of relatively long wavelength, such as primary pumping pressure pulses, and which overcomes the above-mentioned limitations of previous muffler arrangements.
Typically, reciprocating piston compressors include a cylinder block having at least one cylinder bore in which is disposed a reciprocating piston. The piston is operatively coupled, normally through a connecting rod, to the eccentric portion of a rotating crankshaft. Rotation of the crankshaft, which may be operatively coupled to the rotor of an electric motor, induces reciprocation of the piston within the cylinder bore.
Covering an end of the cylinder bore, in abutting contact with the cylinder block directly or through a thin gasket member disposed therebetween, and in facing relation to the piston face, is a valve plate provided with suction and discharge ports which are both in fluid communication with the cylinder bore. Each of the suction and discharge ports are provided with a check valve through which gases are respectively drawn into and expelled from the cylinder bore by the reciprocating piston as the piston respectively retreats from or advances toward the valve plate.
The suction and discharge check valves are normally located adjacent and abut opposite planar sides of the valve plate and may, for example, be of a reed or leaf type which elastically deform under the influence of the gas pressure which acts thereon as the gas enters or leaves the cylinder bore through suction and discharge ports provided in the valve plate, and which are covered by the respective valves. The cylinder head is disposed on the side of the valve plate opposite that which faces the cylinder block, and in prior art compressors the head is in abutting contact with the valve plate, directly or perhaps through a thin gasket member disposed therebetween. Alternatively, the valve plate-interfacing surface of the head may be provided with a machined groove in which a seal is disposed, the seal compressed as the head is abutted to the interfacing valve plate surface.
The cylinder head is normally a die cast aluminum or cast iron component which at least partially defines separate suction and discharge chambers therein. Suction pressure gas is introduced into the head suction chamber through an inlet to the head; and the suction pressure gas is drawn by the retreating piston from the head suction chamber through the suction port of the valve plate, past the suction check valve, and into the cylinder bore, where the gas is compressed to substantially discharge pressure. The discharge check valve prevents gas in the discharge chamber from being drawn into the cylinder bore through the discharge port of the valve plate.
Discharge pressure gas in the cylinder bore is expelled through the discharge port of the valve plate, past the discharge check valve, and into the discharge chamber of the head, from which it is expelled through the outlet of the head. The suction check valve prevents gas in the cylinder bore from being expelled into the suction chamber of the head through the suction port of the valve plate. As noted above, the discharge chamber defined by the head of a reciprocating piston compressor may serve as a type of expansion chamber muffler. Enlarging the volume of this chamber by including such a spacer generally improves the head""s ability to perform as an expansion type discharge muffler and better attenuate noise associated with pulses carried by the compressed gas.
Moreover, a problem experienced with some reciprocating compressors, particularly those in which the discharge gas is conveyed directly from the head discharge chamber through interconnected conduits to a heat exchanger, is that discharge pressure gas within the head discharge chamber does not readily exit the head, resulting in a pressure buildup in the head discharge chamber during compressor operation. Consequently, the cylinder bore may not be fully exhausted of discharge pressure gas at the end of the compression cycle because the buildup of gas within the head discharge chamber inhibits the accommodation therein of gas being exhausted thereinto from the cylinder. Because gas from the previous compression cycle has not been fully exhausted from the cylinder bore, less suction pressure gas can be drawn into the cylinder during the next compression cycle. Thus, the efficiency of the compressor is compromised. Moreover, the temperature of gas on the discharge side of the system, both within the head itself and the high side of the system, may become excessively high as more and more work is expended on the gas already at discharge pressure.
The previously preferred solution to this problem has been to enlarge the size of the head discharge chamber, thereby allowing gas which is exhausted from the cylinder bore to be more easily compressed into, and accommodated by, the head discharge chamber. As noted above, enlargement of this chamber usually also facilitates improvements in noise quality. One approach to enlarging the head""s discharge chamber has been to retool the head. This solution carries with it attendant tooling costs which may not be insubstantial. Further, where a common head design is shared between different compressor models, a newly designed head which solves the problem for one model may not meet the needs (e.g., packaging requirements) of the other model(s), thereby requiring a plurality of head designs to be released and maintained in inventory.
Another approach to enlarging the head""s discharge chamber is to provide a spacer between the valve plate and the existing head, which effectively enlarges the volume of the head discharge chamber (and the suction chamber as well). The spacer comprises a separate component which may be used in one compressor but not another, the two compressor models sharing a common head design. These spacers may be made of plastic or metal.
Previous plastic spacers have had coefficients of thermal expansion which differ substantially from those of the cylinder block and/or the head, and consequently may either shrink and thereby cause a leak across its sealing surfaces, or expand and be overly compressed between the valve plate and head, thereby placing considerable additional stress on the spacer, the head and bolts which extend through the spacer and attach the head and spacer to the cylinder block. If so stressed, the spacer may crack and consequently leak. Plastic spacers do, however, provide the benefits of being lightweight, and providing insulation against thermal conduction between the head and the cylinder block, thereby keeping the discharge gas somewhat cooler and thus reducing the capacity required of the heat exchanger which condenses the high pressure gas to a high pressure liquid. Plastic spacers are also made inexpensively by injection molding techniques.
Previous metal spacers, on the other hand, undesirably promote thermal conduction between the head and the cylinder block, weigh more, and usually are die cast and machined, resulting in a relatively more expensive part vis-a-vis a plastic spacer. A metal spacer, however, may have a coefficient of thermal expansion which avoids the above mentioned shrinkage and stress concerns attendant with plastic spacers. Further, prior plastic and metal spacers alike may require additional, separate gaskets to seal the opposite open spacer ends to the valve plate and head in order to provide a proper seal.
What is needed is an inexpensively produced head spacer for increasing the volume of the discharge chamber of the cylinder head, which provides seals between the head spacer and the valve plate, and between the head spacer and the cylinder head, without the need for additional seals.
Further, it is known to dispose an end cap over the end of the annular motor stator in a low-side hermetic compressor, the end cap covering both the stator end and the end of the motor rotor disposed inside the stator. It is also known to drawn suction pressure refrigerant gas from within the end cap through a suction tube extending therefrom which is in fluid communication with the inlet to a compression mechanism driven by the motor and disposed at the opposite end of the motor stator. Such a configuration is shown, for example, in U.S. Pat. Nos. 5,129,793 (Blass et al.) and 5,341,654 (Hewette et al.), and exemplified by the Model AV reciprocating compressors manufactured by the Tecumseh Products Company of Tecumseh, Mich. It is also known to provide suction mufflers in this tube intermediate the stator end cap and the compression mechanism, as taught by Blass et al. ""793 and Hewette et al. ""654.
A problem with such suction tube arrangements is that their lengths are fixed and particular to stators of a given height. A unique suction tube design must be provided for each different stator height in compressor assemblies which might otherwise be similar, resulting in part complexities and associated inventorying costs and efforts, and additional jigs and fixtures to produce different suction tube assemblies to accommodate these various stators. It would be desirably to provide a single suction tube assembly, with or without a muffler provided therein, which extends between the stator end cap and the inlet to the compression mechanism and can accommodate stators of different heights. Further, it may also be desirable to fix the distance of the muffler from the inlet to the compression mechanism to aid in properly tuning or packaging the muffler, while still accommodating these different stators.
Further still, it is known to resiliently support the motor/compressor assembly, which includes the motor and compression mechanism, within the hermetic shell or housing on a plurality of mounts affixed to the interior of the housing. Typically, these mounts are equally distributed about the interior circumference of the housing or otherwise placed thereabout in a manner which is merely convenient to attachment of the mounts to the motor/compressor assembly.
It is further understood by those of ordinary skill in the art that the housing has natural resonant frequencies that may produce loud, pure, undesirable tones when the housing is vibrated at or near those frequencies. Typically, equally distributing the mounts about the inner circumference of the housing may, at the points of contact therebetween, establish nodes which coincide with at least one of these natural frequencies. Similarly, placement of the mounts merely to facilitate convenient mounting of the motor/compressor assembly may also place these points of contact at nodes of natural frequencies which produce loud tones. Thus, previous compressors do not beneficially place the motor/compressor mounts on the housing in a manner which addresses the noise associated with excitation of these natural frequencies. To do so would reduce or eliminate the housing""s natural resonant frequencies, and reduce the noise produced thereby.
One aspect of such a noise attenuation system for a compression device relates to an improved discharge pulse reduction system which comprises at least one muffler located in a discharge fluid line, the muffler spaced along the discharge line at a distance from a compressor discharge chamber or another upstream muffler which is a particular fraction or multiple of the wavelength of the primary pumping frequency. Thus, the amplitude of the primary pumping frequency, which may be reduced in the above-mentioned compressor discharge chamber or upstream muffler, is further reduced by the muffler placed at the above-mentioned distance therefrom, at which the already reduced amplitude reaches its new maximum value. Thus, the amplitude of the pulse at the primary pumping frequency is twice attenuated, improving the noise and vibration characteristics of the compressor and/or the refrigerant system into which it is incorporated. The muffler(s) may be of the Helmholtz or expansion chamber type.
Accordingly, the present invention provides a compressor assembly including a compression mechanism into which a gas is received substantially at a suction pressure and from which the gas is discharged substantially at a discharge pressure, the gas discharged from the compression mechanism carrying pressure pulses having a particular frequency and wavelength, these pressure pulses being of variable amplitude. A first muffler is provided through which the gas discharged from the compression mechanism flows, and a second muffler is provided in series communication with the first muffler and through which the gas having flowed through the first muffler flows. The first and second mufflers are spaced by a distance which is substantially equal to an odd multiple of one quarter of the wavelength, the amplitude being reduced in response to the gas having flowed through the second muffler.
The present invention also provides a compressor assembly including a compressor mechanism into which a gas is received substantially at a suction pressure and from which the gas is discharged substantially at a discharge pressure, the gas discharged from the compression mechanism carrying pressure pulses having a particular frequency and wavelength, these pressure pulses being of variable amplitude. Also provided is a conduit through which gas substantially at discharge pressure flows, and means for reducing the amplitude of the pressure pulses at locations at which the amplitudes reach their highest absolute values.
The present invention further provides a method for reducing the amplitude of pressure pulses having a particular wavelength in a fluid, including: flowing the pressure pulse-containing fluid through a conduit; attenuating the pressure pulse amplitude at a first location along the conduit; and further attenuating the pressure pulse amplitude at a second location along the conduit distanced from the first location a distance which is substantially equal to an odd multiple of one quarter of the wavelength.
A head spacer is provided for increasing the volume of a discharge chamber in the cylinder head assembly of a reciprocating piston compressor, in which the head spacer is disposed between a valve plate and a cylinder head, and has a plurality of substantially concentric, alternating ridges and valleys disposed around the periphery of first and second end surfaces of the head spacer. When the cylinder head is torqued down onto the cylinder block in response to a compressive load exerted on the cylinder head during the assembly of the cylinder head assembly, the tips of the ridges deform to form a continuous labyrinth seal between the head spacer and the cylinder head, and between the head spacer and the valve plate.
The head spacer may be made from an injection-molded plastic, and has a coefficient of thermal expansion which is substantially similar to the metal components of the cylinder head assembly, such that the head spacer may shrink and/or expand at the same rate as the cylinder block and cylinder head. Further, the plastic from which the head spacer is made provides insulation against thermal conduction between the valve plate and the cylinder head.
In one form thereof, a reciprocating piston compressor is provided, including cylinder block having a cylinder bore; a piston reciprocatingly disposed in the cylinder bore; a cylinder head connected to the cylinder block and partially defining a suction chamber into which gas is received and from which the gas exits into the cylinder bore substantially at a suction pressure, the cylinder head partially defining a discharge chamber into which gas is received from the cylinder bore and from which the gas exits substantially at a discharge pressure; a valve plate having a suction port through which the cylinder bore and the suction chamber fluidly communicate, and a discharge port through which the cylinder bore and the discharge chamber fluidly communicate; a suction check valve disposed over the suction port and past which gas flows from the suction chamber to the cylinder bore, flow from the cylinder bore to the suction chamber being inhibited by the suction check valve; a discharge check valve disposed over the discharge port and past which gas flows from the cylinder bore to the discharge chamber, flow from the discharge chamber to the cylinder bore being inhibited by the discharge check valve; and a spacer disposed between the valve plate and the cylinder head, the spacer having generally opposite first and second end surfaces, each of the first and second spacer and surfaces respectively abutting an interfacing surface of the valve plate and the cylinder head, the spacer partially defining the discharge chamber, a substantial portion of the volume of the discharge chamber located between spacer end surfaces; wherein the first and second spacer end surfaces are each provided with a plurality of substantially concentric ridges having tips, the ridge tips having one of a deformed state and an undeformed state, adjacent ones of the ridges separated by a valley, the ridge tips being placed in the deformed state in response to a compressive load exerted on the spacer between the valve plate and the cylinder head during assembly of the compressor, the deformed ridge tips providing a seal between the first spacer end surface and the valve plate, and between the second spacer end surface and the cylinder head.
In a further form thereof, a cylinder head spacer for a reciprocating piston compressor is provided, including a body portion made of a plastic material and having a substantially open interior extending between first and second end surfaces; and a plurality of substantially concentric, alternating ridges and valleys extending around a periphery of each of the first and second end surfaces, the ridges having one of a deformed state and an undeformed state, the ridges being placed in the deformed state in response to a compressive load exerted on the first and second end surfaces, such that the ridges extend into the valleys and contact adjacent ridges to form sealing surfaces, the sealing surfaces coplanar with the first and second end surfaces.
In another form thereof, a method of assembling a reciprocating piston compressor having a cylinder block with a cylinder bore opening, a valve plate, and a cylinder head, is provided, including the steps of providing a spacer having first and second end surfaces each provided with a plurality of substantially concentric ridges having tips, the ridge tips having one of a deformed state and an undeformed state, adjacent ones of the ridge tips separated by a valley; orienting the valve plate, the spacer, and the cylinder head in a stack arrangement over the cylinder bore opening; and exerting a compressive load on the ridge tips to deform the ridge tips to the deformed state, the deformed ridge tips providing sealing contact between the first spacer end surface and the valve plate, and between the second spacer end surface and the cylinder head.
In a still further form thereof, a method is provided of assembling a cylinder head assembly of a reciprocating piston compressor, the compressor having a cylinder block with a bolt hole therein, including the steps of providing a bolt, a suction leaf plate, a valve plate, and a cylinder head, each of which include a bolt hole therein; providing a spacer having a bolt hole, and first and second end surfaces each provided with a plurality of continuous, alternating ridges and valleys extending around a periphery of each of the first and second end surfaces, the ridges including tips having one of a deformed state and an undeformed state; positioning the suction leaf plate, the valve plate, the spacer, and the cylinder head, respectively, on the cylinder block such that the bolt holes are aligned; inserting the bolt through the bolt holes, and tightening the bolt to exert a compressive load on the ridge tips and deforming the ridge tips to the deformed state, the deformed ridge tips providing sealing contact between the first spacer end surface and the valve plate, and between the second spacer end surface and the cylinder head.
One advantage of the present head spacer is that it is inexpensively produced, and, because the head spacer comprises an individual component, the head spacer may used with existing compressor designs without retooling other components of the cylinder head assembly.
Another advantage is that the labyrinth seal produced by the deformation of the ridge tips of the head spacer obviates the need for additional seals between the head spacer and the valve plate, and between the head spacer and the cylinder head.
A further advantage is that the plastic material of the head spacer both provides insulation against thermal conduction between the cylinder block and the cylinder head, and has a coefficient of thermal expansion substantially similar to the other metal components of the cylinder head assembly to prevent the leakage due to the shrinkage and expansion which is observed with existing head spacers.
Another aspect of the inventive noise attenuation system for a compression device relates a suction tube assembly which extends between the stator end cap and the inlet to the compression mechanism, and may be telescoped in the general direction of the stator""s longitudinal axis to accommodate stators of different heights. Certain embodiments of this suction tube assembly include a muffler, and this muffler may have a location which is fixed relative to the compression mechanism.
Accordingly, the present invention provides a compressor assembly including a compression mechanism having an inlet into which a gas substantially at suction pressure is received, and an outlet from which gas compressed by the compression mechanism is discharged substantially at a discharge pressure. A motor is also included which includes a rotor and a stator, the stator substantially surrounding the rotor and having an end, the rotor operatively coupled with the compression mechanism. An end cap is disposed over the stator end, the end cap having an interior in which is gas substantially at suction pressure. A suction tube of variable length is also provided through which the compression mechanism inlet and the end cap interior are in fluid communication, the suction tube comprising first and second tubes which are in sliding, telescoping engagement, whereby the length of the suction tube may be adjusted through relative axial movement of the first and second tubes.
The present invention also provides a compressor assembly including a compression mechanism having an inlet into which a gas substantially at suction pressure is received, and an outlet from which gas compressed by the compression mechanism is discharged substantially at a discharge pressure, and a motor having a rotor and a stator selected from a plurality of stators of differing heights. The stator substantially surrounds the rotor and has opposite ends distanced by the stator""s height. The rotor is operatively coupled with the compression mechanism. An end cap is disposed over one of the stator ends and has an interior substantially at suction pressure, and first and second telescopingly engaged tubes defining a suction tube which extends axially over at least a portion of the stator height and through which the end cap interior and the compression mechanism inlet are in fluid communication. The suction tube has a length which is varied in response to the relative axial positions of the telescopingly engaged first and second tubes, whereby the suction tube length may be varied to accommodate a different stator alternatively selected from the plurality of stators.
Further, the present invention provides a compressor assembly including a compression mechanism having an inlet into which a gas substantially at suction pressure is received, and an outlet from which gas compressed by the compression mechanism is discharged substantially at a discharge pressure, and a motor having a rotor and a stator selected from a plurality of stators of differing heights. The stator substantially surrounds the rotor and has opposite ends distanced by the stator""s height. The rotor is operatively coupled with the compression mechanism. An end cap is disposed over the stator and has an interior in which is gas substantially at suction pressure, the end cap being distanced from the compression mechanism inlet an amount dependent upon the stator""s height. A tube assembly is provided through which gas is directed from the end cap interior to the compression mechanism inlet, the tube having means for adjusting its length, whereby the compressor assembly could alternatively comprise a different stator selected from the plurality of stators.
Still another aspect of the inventive noise attenuation system for a compression device relates to motor/compressor assembly mounts which are attached to the interior of the compressor housing in a manner which reduces or eliminates natural resonant frequencies of the housing. The mounts are distributed unequally about the inner circumference of the housing and attached thereto a positions which do not coincide with nodes of these frequencies. That is, the mounts are secured to the inside of the housing to interfere with the wave form produced by the natural frequencies in the compressor housing so as to reduce objectionable noise. Resonation of the housing at these natural frequencies is thus prevented, and the compressor quieted.
Accordingly, the present invention provides a compressor assembly including a housing having at least one natural frequency having a wave form with amplitude large enough for the housing, when vibrated at that frequency, to produce an objectionable noise. The natural frequency wave form has a plurality of natural nodes equally distributed about the circumference of the housing and natural anti-nodes located between adjacent natural nodes. A motor/compressor assembly is also provided which includes a compression mechanism in which gas is compressed from substantially a suction pressure to substantially a discharge pressure, and a motor operably engaged with the compressor mechanism. A plurality of mounts are unequally distributed about the circumference of the housing, the motor/compressor assembly being supported within the housing by the mounts. Each mount is attached to the housing at a first point, the first points not coinciding with the natural nodes of the natural frequency wave form. These first points define forced nodes on the circumference of the housing to which the nodes of the natural frequency wave form are forced, and the natural frequency wave form is altered in response to the natural nodes being forced to the forced nodes, whereby the housing is prevented from vibrating at the natural frequency.